This application claims the benefit of Korean Application No. 1999-47750, filed Oct. 30, 1999, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a device in a signal detecting apparatus that reduces cross talk, and more particularly, to a signal detecting apparatus for improving the precision in detecting a tracking error signal and/or a reproduction signal with crosstalk noise greatly reduced.
2. Description of the Related Art
A conventional method for detecting a tracking error signal (TES) is by differential phase detection (DPD). DPD involves detecting tracking errors by receiving light radiated from a light source of an optical pickup device and reflected from a disk.
Referring to FIG. 1, light radiated onto a ROM-type disk is reflected and diffracted into 0th-order maximum and xc2x11st-order maxima by recording marks such as pits (P). After traveling back to the optical pickup, the light received at a photodetector 1 substantially consists of the 0th-order maximum overlapped by xc2x11st-order maxima in a radial direction. As shown, for a high-density disk having narrow tracks, such as a next-generation digital versatile disk (DVD) like an HD-DVD, the 0th-order maximum and xc2x11st-order maxima overlap, while the +1st-order maximum and xe2x88x921st-order maximum do not overlap each other.
The phase signals for the portions where the 0th-order maximum overlaps with the +1st-order maximum and the xe2x88x921st-order maximum have different features than the phase signal of the portion that only receives the 0th-order maximum. Thus, a high-density disk having narrow tracks, if a tracking error signal is detected by a general DPD method in which detection signals of diagonal sectional plates A/C and B/D are simply subtracted, there is a lot of noise in the tracking error signal due to crosstalk between adjacent tracks. In order to detect a tracking error signal with reduced crosstalk noise from adjacent tracks, there has been proposed a method in which an 8-sectional photodetector 20 is used to reduce the cross talk using the device shown in FIG. 2.
As shown in FIG. 2, the 8-sectional photodetector 20 is divided into 4 parts the 4 parts are along a row in the radial direction of a disc. Each part is further divided into 2 parts in the tangential direction of a disk to create a 2xc3x974 matrix. As shown, the respective 2-sectional plates A1/A2, B1/B2, C1/C2 and D1/D2 correspond to the sectional plates A, B, C and D of the photodetector 21 shown in FIG. 1. The sectional plates A2, B2, C2 and D2 are located tangentially inward to A1, B1, C1 and D1, respectively.
The tracking error signal is produced from the detection signals from the 8-sectional photodetector 20 as follows.
Referring to FIG. 3, detection signals a1 and c1 of outer sectional plates A1 and C1 are summed to produce a sum signal (a1+c1). In addition, detection signals a2 and c2 of inner sectional plates A2 and C2 are summed and amplified with a predetermined gain k1 to form amplified summed signal k1(a2+c2). These results are summed to produce the sum signal (a1+c1+k1(a2+c2)), which is amplified by a predetermined gain k2 using amplifier 21.
Likewise, a sum signal (b1+d1) of detection signals b1 and d1 of outer sectional plates B1 and D1 and a signal obtained by amplifying a sum signal (b2+d2) of detection signals b2 and d2 of inner sectional plates B2 and D2 with a predetermined gain k are summed. Then, the signal (k2(a1+c1+k1(a2+c2))) output from the amplifier 21 and the operation signal (b+d1+k(b2+d2)) output from the diagonal sectional plates B1, B2, D1 and D2 are applied to a phase comparator 25 for comparison of phases, to then generate a tracking error signal TES.
As shown, if k=k1=0 and k2=1, the signals applied to the phase comparator 25 are a1+c1 and b1+d1, which corresponds to the case where a phase difference is obtained using a sum signal of detection signals of outer sectional plates arranged in a diagonal direction. Also, if kxe2x89xa00 and k1xe2x89xa00, the signals applied to the phase comparator 25 are a2+c2 and b2+d2, which correspond to the case where a phase difference is obtained using a sum signal of detection signals of inner sectional plates arranged in a diagonal direction.
According to the aforementioned tracking error signal detecting apparatus, since a phase difference is obtained by selectively amplifying the detection signals of inner sectional plates A2, B2, C2 and D2 with predetermined gain factors, and then adding the amplified signals and detection signals of outer sectional plates A1, B1, C1 and D1, a tracking error signal with reduced crosstalk noise can be generated.
Although the conventional tracking error signal detecting apparatus reduces crosstalk noise to a degree, when it is used with a high-density disk having narrow tracks, since the tangential phase characteristics are obscured, the gain of the tracking error signals is very low. Thus, the precision is poor. Basically, the light beams received at the sectional plates positioned at different locations in a tangential direction of a track have different phase characteristics at a starting area and an ending area of a recording mark such as a pit. However, if the detection signals of diagonally adjacent plates are summed as in the conventional tracking error signal detecting apparatus, the tangential phase characteristics are offset, which results in tracking error signals having a low gain and poor precision.
Also, in the conventional tracking error signal detecting apparatus, since the sum signals of detection signals of diagonally adjacent sectional plates are used, a phase difference between the sum signals is offset due to a difference in the depth between pits. Thus, if an objective lens (not shown) is shifted, a large offset may occur to the tracking error signals.
The present invention has been made in view of the points described above, and it is an object of the present invention to provide a signal detecting apparatus with improvement in gain characteristics and/or offset for reduced crosstalk noise.
It is a further object of the present invention to provide a tracking error signal detecting apparatus with improvement in gain characteristics and/or offset due to a difference in the depth between pits by providing an improved sectioning structure of an 8-sectional photodetector with reduced crosstalk noise.
It is a still further object of the present invention to provide a reproduction signal detecting apparatus with improvement in gain characteristics and/or offset due to a difference in the depth between pits by providing an improved sectioning structure of an 8-sectional photodetector with reduced crosstalk noise.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above object, there is provided a tracking error signal detecting apparatus including a photodetector which receives light reflected/diffracted from a recording medium, and a circuit unit which performs operations on detection signals of the photodetector and produces a tracking error signal, wherein the photodetector includes four light receiving regions arrayed counterclockwise, the dividing lines of which are substantially parallel to the radial and tangential directions of the recording medium, each of the four light receiving regions are further bisected to produce an inner sectional plate and an outer sectional plate, the radial widths of which vary along xc2x1 tangential directions from the center of the photodetector, so that 8 inner and outer sectional plates arrayed in a 2xc3x974 matrix are formed, the directions of columns and rows of the sectional plates corresponding to the radial and tangential directions of the recording medium, and wherein the circuit unit compares the phases of the light receiving regions positioned in the same row and then produces a tracking error signal from a phase difference signal.
According to another aspect of the present invention, the circuit unit amplifies at least some of the detection signals of the inner and/or outer sectional plates positioned in one diagonal direction with a predetermined gain, compares phase differences between the amplified signals and at least some of the detection signals of inner and/or outer sectional plates positioned in the other diagonal direction, and detects a tracking error signal from a phase difference signal.
According to another aspect of the present invention, the inner sectional plates are formed such that their widths are relatively narrower at the center of the photodetector and relatively wider along xc2x1 tangential directions.
According to another aspect of the present invention, the lines dividing the inner light receiving regions from the outer sectional plates are preferably curved lines, and the maximum width of each of the inner sectional plates is preferably larger than the radius of received 0th-order maximum.
According to another aspect of the present invention, a reproduction signal detecting apparatus for accomplishing the above and other objects of the present invention may include a photodetector which receives light reflected/diffracted from a recording medium, and a circuit unit which performs operations on detection signals of the photodetector and produces a reproduction signal, wherein the photodetector includes four light receiving regions arrayed counterclockwise, the dividing lines of which are substantially parallel to the radial and tangential directions of the recording medium, each of the four light receiving regions are further bisected to produce an inner sectional plate and an outer sectional plate, the radial widths of which vary along xc2x1 tangential directions from the center of the photodetector, so that 8 inner and outer sectional plates arrayed in a 2xc3x974 matrix are formed, the directions of columns and rows of the sectional plates corresponding to the radial and tangential directions of the recording medium, and wherein the circuit unit includes an amplifier for amplifying a sum signal of detection signals of the outer sectional plates, and an adder for adding a sum signal of detection signals of the inner sectional plates and the output signal of the amplifier.
According to another aspect of the present invention, the circuit unit may further include a time delay for time-delaying detection signals of the inner and/or outer sectional plates positioned in one row.